1. Field of the Invention
The invention generally relates to wireless communication technologies, and more particularly, to methods for network selection by mobile communication devices supporting a plurality of Radio Access Technologies (RATs) and a plurality of radio frequencies.
2. Description of the Related Art
With growing demand for ubiquitous computing and networking, various Radio Access Technologies (RATs) have been developed, such as the Global System for Mobile communications (GSM) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (W-CDMA) technology, High Speed Packet Access (HSPA) technology, Interim Standard 95 (IS-95) technology, Code Division Multiple Access 2000 (CDMA2000) technology, CDMA2000 1× Evolution-Data Optimized or Evolution-Data (1× EV-DO) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access (WiMAX) technology, Long Term Evolution (LTE) technology, Time-Division LTE (TD-LTE) technology, LTE-Advanced (LTE-A) technology, and others.
Generally, a mobile phone only supports one RAT for providing users with the flexibility of mobile communications at all times via the supported RAT. However, due to the complexity of various network deployments, so-called multi-RAT mobile phones have been developed, which generally support two or more RATs and radio frequencies, and select one of the RATs for obtaining mobile services. Since multi-RAT mobile phones support multiple RATs and radio frequencies, the Public Land Mobile Network (PLMN) selection procedure will inevitably take a long time to complete a full scan for all of the supported RATs on each supported radio frequency. This may create an unfavorable situation where a multi-RAT mobile phone enters an area with very poor signal quality only for a short time (e.g., passing through a tunnel). For example, once the multi-RAT mobile phone detects that the signal coverage has been lost, the PLMN selection procedure will be performed for a full scan. Later, even if the multi-RAT mobile phone swiftly enters an area with signal coverage of those that have been scanned in the early stage of the full scan, it will still continue the full scan with the un-scanned RATs and radio frequencies and cannot regain normal services from the available area using the scanned RAT and radio frequency. The delay for regaining normal services is expected to get worse especially when the number of supported RATs and radio frequencies increases, and the longer the delay is, the higher the chance of a service breakup (e.g., TCP/IP-based application).
Therefore, it is desirable to have a more sophisticated way of network selection that can reduce the time to obtain/regain normal services.